Can you give me a ballpark figure on replacing a head gasket on a older Craftsman riding lawn mower...

There are many variables, since you didn't give any specifics. if it is an older, single cylinder, L-head engine, labor would be roughly 1/2 hour; if an older twin, L-head, about 1 hour; if it's a kohler, add about 1/2 hour; if it's a single, OHV, about 1 hour; if a twin OHV, 1 1/2 hours; if a kohler, add 1/2 hour. each shop has it's own labor rate. flat rate manuals will vary and are not realistic when dealing with old, possibly rusted or frozen bolts, which will increase the cost of repair. a new head gasket will usually cost between $5 to $30, depending on which engine you have. {some older craftsmans had a briggs laid sideways or an onan. these will require a lot more work and the labor would be higher]